Oxidation resistant iron base alloy compositions

Abstract

This invention relates to iron-base alloy compositions, nickel containing austenitic ferrous alloy compositions (especially low nickel compositions) and dopants added to low nickel austenitic alloys as a means of improving the elevated temperature oxidation resistance of the resultant material.

I claim: 
     
       1. A crystalline iron-base alloy composition exhibiting improved resistance to oxidation, comprising: (i) iron;   (ii) chromium;   (iii) silicon;   (iv) magnesium at a level of about 0.1 to about 1.5 percent, by weight of the final composition;   (v) calcium at a level of about 0.1 to about 1.5 percent, by weight of the final composition; and   (vi) an amount of a dopant element sufficient to show a significant and reproducible improvement in one or more oxidation resistant properties of the final composition selected from the group consisting of sodium, lithium, potassium and mixtures thereof.   
     
     
       2. A composition according to claim 1 further comprising barium. 
     
     
       3. A composition according to claim 1 further comprising yttrium. 
     
     
       4. A composition according to claim 1 further comprising lanthanum. 
     
     
       5. A composition according to claim 1 further comprising cerium. 
     
     
       6. A composition according to claim 1 further comprising aluminum. 
     
     
       7. A composition according to claim 1 further comprising beryllium. 
     
     
       8. A composition according to claim 1 further comprising strontium. 
     
     
       9. A composition according to claim 1 wherein the dopant element is present at a level of at least about 0.02 percent, by weight of the final composition. 
     
     
       10. A composition according to claim 9 wherein the dopant element is present at a level of about 0.05 to about 5 percent, by weight of the final composition. 
     
     
       11. A composition according to claim 10 wherein the dopant element is present at a level of about 0.1 to about 3.5 percent, by weight of the final composition. 
     
     
       12. A composition according to claim 11 wherein the dopant element is present at a level of about 0.1 to about 2.0 percent, by weight of the final composition. 
     
     
       13. A composition according to claim 1 wherein said chromium is present at a level of about 10 to about 30 percent, by weight of the final composition. 
     
     
       14. A composition according to claim 1 wherein the dopant element comprises lithium. 
     
     
       15. A composition according to claim 1 wherein the dopant element comprises sodium. 
     
     
       16. A composition according to claim 1 wherein the dopant element comprises potassium. 
     
     
       17. A composition according to claim 1 further comprising manganese. 
     
     
       18. A composition according to claim 1 further comprising cobalt. 
     
     
       19. A composition according to claim 1 further comprising nitrogen. 
     
     
       20. A composition according to claim 1 further comprising nickel. 
     
     
       21. A composition according to claim 20 wherein said nickel is present at a level of about 5 to about 15 percent, by weight of the final composition. 
     
     
       22. A crystalline iron-base alloy composition exhibiting improved resistance to oxidation, comprising: (i) iron;   (ii) chromium;   (iii) silicon;   (iv) an amount of a first dopant element sufficient to show a significant and reproducible improvement in one or more oxidation resistant properties of the final composition selected from the group consisting of magnesium, calcium, and mixtures thereof; and   (v) a second dopant element selected from the group consisting of sodium at a level of about 0.1 to about 0.5 percent, by weight of the final composition, lithium at a level of about 0.1 to about 0.5 percent, by weight of the final composition, potassium at a level of about 0.5 to about 1.0 percent, by weight of the final composition, and mixtures thereof.   
     
     
       23. A composition according to claim 22 further comprising barium. 
     
     
       24. A composition according to claim 22 further comprising yttrium. 
     
     
       25. A composition according to claim 22 further comprising lanthanum. 
     
     
       26. A composition according to claim 22 further comprising cerium. 
     
     
       27. A composition according to claim 22 further comprising aluminum. 
     
     
       28. A composition according to claim 22 further comprising beryllium. 
     
     
       29. A composition according to claim 22 further comprising strontium. 
     
     
       30. A composition according to claim 22 wherein the first dopant element is present at a level of at least about 0.02 percent, by weight of the final composition. 
     
     
       31. A composition according to claim 22 wherein the first dopant element is present at a level of about 0.05 to about 5 percent, by weight of the final composition. 
     
     
       32. A composition according to claim 31 wherein the first dopant element is present at a level of about 0.1 to about 3.5 percent, by weight of the final composition. 
     
     
       33. A composition according to claim 32 wherein the first dopant element is present at a level of about 0.1 to about 2.0 percent, by weight of the final composition. 
     
     
       34. A composition according to claim 22 wherein said chromium is present at a level of about 10 to about 30 percent, by weight of the final composition. 
     
     
       35. A composition according to claim 22 wherein the second dopant element comprises lithium. 
     
     
       36. A composition according to claim 22 wherein the second dopant element comprises sodium. 
     
     
       37. A composition according to claim 22 wherein the second dopant element comprises potassium. 
     
     
       38. A composition according to claim 22 wherein the first dopant element comprises calcium. 
     
     
       39. A composition according to claim 22 wherein the first dopant element comprises magnesium. 
     
     
       40. A composition according to claim 22 further comprising nickel. 
     
     
       41. A composition according to claim 40 wherein said nickel is present at a level of about 5 to about 15 percent, by weight of the final composition. 
     
     
       42. A composition according to claim 22 further comprising cobalt. 
     
     
       43. A composition according to claim 22 further comprising manganese. 
     
     
       44. A composition according to claim 22 further comprising nitrogen. 
     
     
       45. A crystalline iron-base alloy composition exhibiting improved resistance to oxidation consisting essentially of: (i) iron;   (ii) at least one alloy element selected from the group consisting of nickel, chromium, molybdenum, manganese, silicon, carbon, vanadium, cobalt, copper, nitrogen, aluminum, titanium, zirconium, and mixtures thereof;   (iii) magnesium at a level of about 0.1 to about 0.5 percent, by weight of the final composition;   (iv) calcium at a level of about 0.1 to about 0.5 percent, by weight of the final composition; and   (v) an amount of a dopant element sufficient to show a significant and reproducible improvement in one or more oxidation resistant properties of the final composition selected from the group consisting of sodium, lithium, potassium and mixtures thereof.   
     
     
       46. A composition according to claim 45 wherein the dopant comprises lithium at a level of 0.1 to about 0.5 percent, by weight of the final composition. 
     
     
       47. A composition according to claim 45 wherein the dopant comprises sodium at a level of 0.1 to about 0.5 percent, by weight of the final composition. 
     
     
       48. A composition according to claim 45 wherein the dopant comprises potassium at a level of about 0.1 to about 1.0 percent, by weight of the final composition. 
     
     
       49. A crystalline iron-base alloy composition exhibiting improved resistance to oxidation consisting essentially of: (i) iron;   (ii) at least one alloy element selected from the group consisting of silicon, nickel, chromium, manganese, cobalt, nitrogen, and mixtures thereof; and   (iii) magnesium, calcium, lithium, sodium, and potassium, wherein said magnesium is present at a level of about 0.1 to about 0.5 percent, said calcium is present at a level of about 0.1 to about 0.5 percent, said lithium is present at a level of about 0.1 to about 0.5 percent, said sodium is present at a level of about 0.1 to about 0.5 percent, and said potassium is present at a level of about 0.1 to about 1.0 percent by weight of the final composition.